If the MG soil you are using is the moisture retaining one I wouldn't use it. I would use an all purpose potting soil... I like to add some slow release fertilizer when I plant. use a pre-moistened soil. and don't water it again until it's completely dry or the plant is actively growing leaves... too much moisture as it's coming out of dormancy is what causes the rot...

If you can I would use a clay pot. these dry the soil a little faster. When the plant is actively growing.. water freely.. however let it dry slightly between watering. fertilize with a weak fertilizer every second watering. and I usually stop feeding mid to late summer.. you want the tuber to harden off before digging.